It is widely acknowledged that heat is produced during operations of electronic devices such as central processing units (CPUs). The heat produced must be quickly removed to ensure the CPUs working normally. Typically, a heat sink is provided to a CPU for removing heat from the CPU. In order to keep the heat sink into close contact with the CPU, a locking device is generally required.
FIG. 8 shows a conventional locking device for securing a heat sink 40 to a CPU 100 mounted on a printed circuit board (PCB) 10. The locking device comprises a rectangular retention frame 20, four fastening pins 30 and a wire clip 50. Four retaining holes 12 are defined in the PCB 10 surrounding the CPU 100. Four positioning holes 28 are defined at four corners of the retention frame 20 in alignment with the retaining holes 12 of the PCB 10. A pair of ears 29 is diagonally formed from the retention frame 20 at opposite sides thereof. The clip 50 comprises an elongated pressing beam 52 and a pair of locking feet 54 extending from opposite ends of the pressing beam 52. In assembly, the fastening pins 30 respectively pass through the positioning holes 28 of the retention frame 20 and engage with the PCB 10 in the retaining holes 12 to thereby hold the retention frame 20 on the PCB 10. The clip 50 is positioned on the heat sink 40 with the locking feet 54 engaging with the ears 29 and the pressing beam 52 abutting against a chassis 42 of the heat sink 40 to thereby firmly secure the heat sink 40 to the CPU 100. However, the locking device is only applicable for attachment of the heat sink 40 to a PCB with retaining holes in alignment with the positioning holes 28 of the retention frame 20. When a PCB having a configuration of retaining holes different from the above-mentioned is used, the locking device becomes disqualified.